In recent years, for the sake of the environment, there has been proposed an image forming apparatus which forms an image on a sheet-like medium (hereinafter referred to as a “sheet”) such as paper and the like with decolorable image forming agent so that the printed paper can be reused. The toner material used as the decolorable image forming agent has a function of being decolored through, for example, external stimuli such as temperature, light having a specific wavelength, pressure and the like. The image formed with the decolorable toner is decolored by a given decoloring device. Thus, a user can reuse the sheet repeatedly.
However, there is a case in which the difference in image density between the image formed with the decolorable toner and the image formed with the non-decolorable toner is noticeable.